I have a 2003 Vulcan 1600 Classic with 24k miles on it. Sometimes when I park it after a good day's ride I come back to find a small drip of oil on the ground. Never very big, the size of a quarter at most. It appears to come from the black rubber boot where the driveshaft meets the engine. There was even a little oil on the very bottom of the driveshaft cover once or twice. I took the left sidecover of the engine off, thinking it was the clutch pushrod seal like I have read several times on this forum, but that appeared to be in good shape and there was no oil inside that cover (I was expecting it to be a mess). I also removed the plug on the rear, just to check if that was leaking and the gear oil was traveling down the driveshaft cover to the engine, but that did not appear to be the case either. It didn't appear to be gear oil anyway, it looked like engine oil.

The weird thing is that this only happens very rarely and I don't really see any pattern to it. Is it possible I put too much oil in? I followed the capacity on the sticker right on the block at the filler port. But I think that I read somewhere there is a pressure relief valve on the back of the engine near the drive shaft. FWIW I have one of the early 03's with the cartridge style oil filter on it, don't know if that has any bearing on anything. Could that rubber boot on the driveshaft have gone bad? It appears to be in good shape but who knows. Is it the pushrod seal, and it is in fact leaking even though there was no oil on the sidecover?

The first time it leaked was back in May, and it has only done it a few times since then, so I rode all year and just kept an eye on it. I'm actually not even sure when the last time it did it was. But since winter is upon us I figure it's a good time to go after it.

Can't really answer your question but if your bike is 9 years old it's time to grease the driveshaft splines and swingarm bearings anyhow. It's not as hard as it sounds and while you have everything apart you can inspect the driveshaft universal joint seal and final drive seals for oil leaks.